Electrolytic cell



July 29, 1941. J. c. THOMPSON ELECTROLYTIC CELL Filed April 16, 197

m4 lI IIl/II INVENTOR ATTOR N Patented July 29, 1941 ELECTROLYTIC CELL John Christian Thompson, Port Reading, N. J., assignor to The American Metal Company, Limited, New York, N. Y., a corporation of New York Application April 16, 1937, Serial No. 137,157

4 Claims. (Cl. 204-252) This invention relates to improvements in electrolytic cells, that is, to apparatus wherein a desired metal is selectively dissolved from a crude alloy including that metal, and is then electrodeposited from the solution in pure crystalline form for collection and subsequent use.

The principal object of the invention is to provide a cell of this general character in which the anode compartment is so disposed with respect to the cathode plate that crystals of metal electro-deposited on the latter element during the course of the process may be collected and removed without necessitating a shifting or tilting of the compartment, nor a shutting down of the cell. This, at once, eliminates continual rubhing of the compartment frame against the sides of the tank of the cell, and of the anode plates against the fabric filter bottom. Both make for a reduction in the upkeep cost of the cell; and

the latter prevents loss of valuable anode mud,

and contamination of the deposited metal by such mud. Furthermore, since this cell may be operated almost continuously, its yield of refined product is somewhat better than that obtained from presently available ones.

It is a further object of the invention to provide a cell in which the entire weight of the anode compartment, and of its contents, is carried 1 directly by a plurality of supporting rodsfextending across the tank at points below the normal electrolyte level thereon. Accordingly the comof Fig. 1 looking in the direction indicated by the arrows.

Considering the drawing, wherein like reference numerals identify like parts, the cell comprises,

in essence, an open topped tank l0 having an electrically conductive bottom adapted to serve as a cathode plate ll upon which crystals of pure metal may be deposited, and an anode compartment l2 supported in the tank and partially immersed in the electrolyte [3, so that the latter may pass through its filter bottom and attack.

and dissolve the desired metal from the plates of alloy 15.

In the preferred embodiment the tank It is castfrom concrete or the like so as to have side and end walls 15 and I1, respectively, of substantially uniform height, and a bottom l8 which slopes, gently and uniformly lengthwise of the tank so that one of its ends is deeper than the other. The inner surface is then coated with pitch, Harvel paint, or other material capable of withstanding the corrosive action of the electrolyte, as indicated at l9; and the bottom is covered with a thin layer of electrically conductive material adapted to serve as a cathode plate I l. Preferably the latter element is formed from one or more thin sheets of graphite or ordinary carbon, laid in pitch or similar material.

The anode compartment I 2, according to the preferred embodiment, comprises an open-topped rectangular frame 20, usually made of hard wood or the like, having a width slightly less than the comparable dimension of the tank and of a length which is approximately equal to'half that of the tank; and a filter bottom of canvas or other comparable material which will allow free movement of the electrolyte from the tank to the compartment without permitting a like movement of the deposited metallic crystals, or of the slime left in the compartment as a result of the dissolution of the alloy. In the preferred embodiment the filter bottom comprises a sheet of canvas 3i sewed into box-like form and shrunk over the outer surface of the frame; and a muslin liner 2| having its edges lapped over the dowel pins 22 so that it may be removed whenever the occasion demands.

This compartment l2, as may be seen in the drawing, is disposed in the deep end of the tank with its filter bottom submerged in the liquid electrolyte; and it is supported upon a plurality of smooth glass rods 23 each extending transversely of the tank'and having its opposite ends resting upon the oppositely disposed ledges 24 constituting integral parts of the side walls I6.

Each such ledge, as can be seen, extends along side walls of the tank, and not by the frame of the anode compartment itself.

The advantages of the present cell may best be understood by a consideration of the operation thereof, and for this purpose it will be assumed that pure silver is being refined from dor, a crude alloy of gold and silver. In such instance the electrolyte l3 will comprise a solution of copper nitrate, silver nitrate and a trace of free nitric acid, and the anode of the cell will comprise a plurality of plates of dor resting on the filter bottom of the anode compartment in electrical contact with each other. A silver contact plate 26 is disposed upon one of the. anode plates 25, and a like silver plate 21 is placed upon the cathode ll. Then, upon the flow of current through the electrolyte from any desired source. crystals of pure silver 28 will be deposited on the cathode plate in that area immediately under the anode compartment; and the silver content of the solution will be constantly replaced by the dissolution of the silver component of the dor bars, all in the well understood manner. Since the electrolyte has no efiect whatsoever upon the gold component of the dor, the latter will remain in the anode compartment, as a very fine mud or slime; and the filter bottom will serve to prevent contamination of the pure silver crystals on the cathode by this gold mud.

The silver component of the dor comprises a very high percentage of the total. Thus, in commercial practice it is necessary to remove the deposited silver from the cathode at intervals of about four hours, while the gold content is so small that it may be allowed to accumulate in the anode compartment for three or four days before removal is necessary.

The removal of the silver crystals has heretofore. been a source of some trouble. This has been due in large part to the fact that the construction of the cell was such as to necessitate a tilting of the anode compartment in order to get at the deposited crystals. With the present cell, however, this removal process is very simple. It is only necessary to insert a long handled scraper 29 under the anode compartment and drag the crystals up into the open end of the tank, as indicated at 30. It will be seen that the slope of the anode compartment with respect to the horizontal permits this insertion of the scraper without in any way disturbing the compartment; and that the comparably slop-ed bottom establishes a parallel relationship between the cathode and the anode so that the current density across the cell may be substantially uniform.

In practice it has been found that the slope of the anode compartment, and of the bottom, should. be about four or five degrees, but in certain casesthis may be increased to eight, or even twelve degrees. It is only necessary that this slope shall be such as to permit the insertion of the scraper under the anode compartment without disturbing the latter; and that the slope of the bottom shall not be suflicient to. cause the crystals raked up into the pile 30 to roll down hill. Further, it is highly desirable to maintain an even slope, whatever it may be, from one end of the bottom to the other so that there may be no sharp breaks tending to force the rake handle suddenly upwardly.

The gold mud must be removed, as above men tioned, at regular, but infrequent, intervals. When such becomesnecessary, the cell is cut out of its bank (i. e., the current is cut off), and the compartment is raised sufliciently to drain all of the electrolyte. Then the muslin liner 2|, containing the finely divided anode slime, is physically removed from the frame and is replaced with a new one. It is highly important that the liner, at the time of removal, shall be free from small holes or tears through which the slime may sift to contaminate the deposited metal; and in the assumed case, to result in the loss of valuable gold. The construction of the cell, as above defined, largely avoids any such possibility by eliminating the necessity for continual shifting of the compartment, and consequent rubbing of the muslin by the crude metal anode plates.

With the exception of shut-downs for mud removal as above outlined, and for such repair as from time to time becomes necessary, this cell may be operated continuously. Thus, its yield of deposited product will be greater than that obtained from cells (of the type now available) which must be cut-out of circuit every few hours.

A. further advantage of the present invention is to be found inthe fact that the entire anode compartment rests directly upon the supporting rods 23; and that the weight of the anode plates is likewise carried. directly by these rods. No strain of any kind is imposed upon the wooden compartment frameit might, for descriptive purposes, be said to float in the tank-and hence it is not subject to any particular wear and tear.

Since certain changes may be made in the construction which are well within the skill of the ordinary mechanic, it is intended that the foregoing shall be construed in a descriptive rather than in a limiting sense.

What I claim is:

1. In an electrolytic cell, a tank having side walls and a substantially evenly sloping bottom, a plurality of smooth surfaced supporting rods disposed inspaced relation across the tank adjacent one endthereof with their opposite ends supported directly by the longitudinal side walls of the tank at points beneath the normal level of electrolyte in said tank, said rods lying in a plane which is parallel to the bottom and being wholly submerged in electrolyte in said tank; a

cathode plate extending over said bottom; an anode compartment consisting of a single frame having an open top and a woven fabric bottom, said compartment being removably supported in said tank by having its bottom resting upon said rods; and an anode plate disposed in said compartment and supported by said rods.

2. An electrolytic cell comprising a tank having side Walls and a bottom, supporting ledges formed.- along its opposite side walls comprising a part, of the tank. and extending from one end of the tank approximately to the middle thereof with their upper supporting surfaces lying beneath the normal level of electrolyte in said tank; a plurality of smooth surfaced supporting rods disposed in spaced relation across the tank with their opposite ends resting on said ledges; an anode compartment consisting of a single frame having an open top and a fabric bottom, said frame being removably supported in said tank with its bottom resting on said supporting rods; a cathode plate extending over the bottom of said tank beneath said compartments; and an anode in said compartment and supported by said rods.

3. An electrolytic cell according to claim 2, further characterized in that each of said ledges has a series of slots formed therein at regularly spaced intervals, which slots are open at their upper endsto receive the ends of said rods and have their bottoms all lying in'a common plane spaced above the bottom of said tank and beneath the electrolyte level therein; in that said frame comprises side and end Walls to which said fabric bottom is secured; and by the provision of a fabric liner removably secured in said frame.

JOHN CHRISTIAN THOMPSON. 

